Examples of a circuit that outputs a large amplitude signal in order to emit a radio wave from an antenna include a power amplifier.
As illustrated in FIG. 10, as a power amplifier, there has been widely used a circuit that includes N channel MOS transistor 801, inductor 802, and band-pass filter 803 and that is configured to use a pulse wave as an input signal. In this configuration, however, the output signal of the power amplifier becomes a signal that is similar to a pulse waveform and that includes a harmonic wave component.
As illustrated in FIG. 11, there is another pulse power amplifier that uses an inverter including N channel MOS transistor 902 and P channel MOS transistor 901. This configuration also generates output including a harmonic wave.
Conventionally, a power amplifier has been proposed that independently sets the duty ratio and phase of an input pulse wave of each of a plurality of amplifiers and that combines the output of the plurality of amplifiers, in order to reduce odd-order harmonic waves in particular (for example, see Patent Literature (hereinafter, abbreviated as PTL) 1).
FIG. 12 is a circuit diagram of the power amplifier described in PTL 1, and FIG. 13 is a timing chart illustrating the signal waveform of each component of the power amplifier in FIG. 12. The power amplifier in FIG. 12 combines the output of an inverter including N channel MOS transistor 1001 and P channel MOS transistor 1002, and the output of an inverter including N channel MOS transistor 1003 and P channel MOS transistor 1004 to form an output signal. As illustrated in FIG. 13, the duty ratios and phases of timing signals A10, B10, and C10 to respective components are independently set to thereby make the output waveform similar to a sine wave and thus to reduce odd-order harmonic waves.